From a presentation that may be found on http://www.incaweb.org/nato-asi_rsv/BUSCH_1.pdf by BUSCH, Rainer. Renewable Raw Materials for the Chemical Industry. NATO ASI “New Organic Chemistry Reactions and Methodologies for Green Productions”. 30 Oct.-5 Nov. 2006, it is known to use 5-hydroxymethylfurane (5-HMF) as platform chemical for the preparation of 2,5-furandicarboxylic acid. With respect to the synthesis of this platform chemical, Dr. Busch mentions the production of 5-HMF from glucose or fructose (renewables) and suggests the oxidation of 5-HMF into 2,5-FDCA. However, at the same time, Dr. Busch mentions that there is still much development work required. Moreover, Dr. Busch suggests the preparation of segmented thermoplastics from renewables, having hard block(s) composed of the polyamide of 2,5-dicarboxylic acid and 1,6-hexanediamine, and having soft block(s) composed of the polyether of 1,4-butanediol. Dr. Busch, on the other hand has not prepared any of the polymers suggested in his presentation.
In GB 621971 polyesters (and polyester-amides) are prepared by reacting glycols with dicarboxylic acids of which at least one contains a heterocyclic ring, such as 2,5-FDCA. In place of the dicarboxylic acids, the dialkyl or diaryl esters thereof may be used, in particular where acids are used which tend to be unstable and to develop carbon dioxide under the conditions of the reaction. Moreover, when using di-esters, it is of advantage to include in the reaction mixture an ester-interchange catalyst, as for example an alkali metal, magnesium or tin. Indeed, in Examples 1 and 2 of this reference, dimethyl-2,5-furandicarboxylate is reacted with an excess of ethylene glycol in the presence of sodium dissolved in methanol and magnesium. A crystalline mass product is obtained, which is then at a temperature of 190 to 220° C. and under reduced pressure converted into a polymer.
In HACHIHAMA, Yoshikazu, et al. Syntheses of Polyesters containing Furan Ring. Technol. Repts. Osaka Univ. 1958, vol. 8, no. 333, p. 475-480. it is mentioned that many aromatic polyesters are known, but only polyethylene terephthalate is in commercial production. In this paper polyesters are produced by condensation of 2,5-FDCA with various α,ω-glycols. According to this paper, ester interchange has proved to be the most convenient method for 2,5-furandicarboxylic acid polyesters, since the acid is difficult to be purified. The ester interchange reaction is promoted by the presence of a catalyst such as litharge, a natural mineral form of lead(II) oxide. The polymers made, however, were brown to greyish white.
In WO 2007/052847 polymers are provided, having a 2,5-furandicarboxylate moiety within the polymer backbone and having a degree of polymerization of 185 or more and 600 or less. These polymers are made in a two step process involving the esterification of the 2,5-FDCA with a diol first, and a second step involving polycondensation through an ester exchange reaction. The first step is carried out catalytically at a temperature within the preferred range of 150 to 180° C., whereas the polycondensation step is carried out under vacuum at a temperature within the preferred range of 180 to 230° C. A particularly preferred example of a catalyst effective in both steps is titanium alkoxide. Indeed, in the examples 2,5-FDCA is reacted first with a diol, using a tin catalyst and a titanium catalyst. The intermediate product is then purified by dissolving the same in hexafluoroisopropanol, reprecipitation and drying, followed by solid state polymerization at a temperature in the range of from 140 to 180° C. Not disclosed, but found by the current inventors, is that the intermediate product produced by the process of this reference is darkly colored. This is therefore the reason for the purification step. This essential purification step, and in particular when using hexafluoroisopropanol, is a serious drawback of this process, severely limiting the commercialization thereof. The problem vis-à-vis this recent development is to produce polymers having a 2,5-furandicarboxylate moiety within the polymer backbone, at high molecular weight and without colored impurities, without having to use a purification step.
In MOORE, J. A., et al. Polyesters Derived from Furan and Tetrahydrofuran Nuclei. Macromolecules. 1978, vol. 11, no. 3, p. 568-573. are described. Polymers were prepared using 2,5-furandicarbonyl chloride as monomer. As a result, polymers in the form of a white precipitate having a very low intrinsic viscosity (and hence low molecular weight) were obtained. In addition, a polymer was prepared from 1,6-hexane diol and dimethyl-2,5-furan dicarboxylate, using calcium acetate and antimony oxide as catalyst. The number average molecular weight was low (less than 10,000), whereas the molecular weight distribution was relatively high (2.54 instead of about 2). Moreover, the product was greenish. Again, from this reference it would appear near impossible to produce polymers having a 2,5-furandicarboxylate moiety within the polymer backbone, at high molecular weight and without colored impurities, without having to use a precipitation and/or purification step.
In U.S. Pat. No. 4,014,957 thermoplastic moulding compositions of (A) 99.5 to 80% by weight, of at least one amorphous linear polyamide and (B) 0.5 to 20% by weight of at least one segmented thermoplastic elastomeric copolyester are disclosed. According to this patent segmented thermoplastic elastomeric copolyesters are known, which may be prepared from various dicarboxylic acids, including 3,4-FDCA.
In EP 0294863 A aromatic polyesters containing units with two carbonyl groups and having liquid crystalline properties are disclosed. The aromatic polyesters are characterized in that the polyesters contain heterocyclic units with two carbonyl groups. Preferably these units are derived from furandicarboxylic acid. The aromatic polyesters show a considerable reduction in melting temperature, rendering the polyester more processable. The heterocyclic unit acid can be a 2,5-FDCA, a 2,4-FDCA or a 2,3-FDCA or a derivative of these acids. The polyester according to this reference can be prepared in a process known per se, for example via condensation or esterification of the reactive derivatives of the components to be used. Preferably a condensation reaction is applied; the reaction of the monomers takes place between 50° C. and 350° C., preferably in an inert atmosphere such as nitrogen or argon, followed by a polycondensation reaction, at increased temperature and reduced pressure, which results in a polycondensate with the desired degree of polymerization. According to this reference it is possible to effect the condensation or esterification and the polycondensation reaction in the presence of a catalyst. Magnesium, manganese, sodium, potassium and/or zinc acetates are preferred.
In U.S. Pat. No. 5,112,915 copolyetherester molding compositions are described that comprise a copolyetherester and a modifying amount of a modulus reducing rubbery interpolymer comprising a crosslinked (meth)acrylate rubbery phase and an interpenetrating, crosslinked styrenic resin phase. According to the reference, suitable thermoplastic copolyetheresters (A) include both random and block copolymers. In general these are prepared by conventional esterification/polycondensation processes from (i) one or more diols, (ii) one or more dicarboxylic acids, (iii) one or more long chain ether glycols, and optionally, (iv) one or more lactones or polylactones. Dicarboxylic acids (ii) which are suitable for use in the preparation of the copolyetheresters include aliphatic, cycloaliphatic, and/or aromatic dicarboxylic acids. 3,4-FDCA is mentioned as a suitable acid to be used.
In U.S. Pat. No. 5,958,581 a polyester film made from a polymer having ethylene glycol moieties, isosorbide moieties and terepthaloyl moieties, and the method of making the film is described. The polyester of this reference may be formed by melt polymerization, which is carried out in two stages. First, the diols (e.g., ethylene glycol) are mixed with the dimethyl ester of the diacid (e.g., dimethyl terephthalate) in the presence of an ester interchange catalyst, which causes exchange of the ethylene glycol for the methyl group of the dimethyl esters through a transesterification reaction. The reaction is gradually heated to about 250° C. until methanol evolution stops. Preferred catalysts for ester interchange include Mn(OAc)2, Co(OAc)2, and Zn(OAc)2, where OAc is the abbreviation for acetate, and combinations thereof. The second stage of the reaction is commenced by adding a polycondensation catalyst. An example of a polycondensation catalyst is antimony (III) oxide, which may be used at a level of 100 to about 400 ppm.
The polycondensation reaction is typically carried out at a temperature from about 250 to 285° C. The current inventors found that when using these conditions when producing polymers having a 2,5-furandicarboxylate moiety within the polymer backbone, it was impossible to obtain a polymer having a high molecular weight without suffering from an abundance of colored impurities.
In U.S. Pat. No. 6,737,481 a polymer comprising poly(alkylene-co-dianhydrosugar ester) dicarboxylate and its preparation is described. The processes of this reference avoid the problems created by the slow reaction rate for direct esterification or transesterification of isosorbide with terephthalic acid or dimethylterephthlate. Diacids that may be used in this process include 2,5-FDCA. The procedure, here described for isophthalic acid and isosorbide, involves heating a 0 to 100 mole % excess of isosorbide, with isophthalic acid in the presence of about 90-140 micrograms/g tin in the form of a suitable catalyst, such as n-butylstannoic acid under an inert gas atmosphere. The temperature is preferably from about 240 to about 260° C. and heating is continued until no further water evolves, typically for about 1 to 2 hours, indicating the end of the esterification reaction.
Catalysts that may be used in this process are generally known in the art, and include salts of U, Ca, Mg, Zr, Mn, Zn, Pb, Sb, Sn, and Ti, such as acetate salts and oxides, including glycol adducts, and Ti alkoxides and chelates.
The preferred molar ratio of catalyst to diacid is about 1:1,000 to about 1:7,300. A catalyst can also be used to enhance esterification or transesterification, and polycondensation catalysts are said to be particularly useful in transesterification.
From the above references, it would therefore appear that polymers and copolymers of 2,5-FDCA can be made by simply substituting terephthalic acid as diacid monomer and using 2,5-FDCA instead. However, the current inventors found that to be rather problematic.
In JP2008291244 a method for producing polyester resin including furan structure is provided. The method for producing a polyester resin including a furan structure comprises performing ester exchange reaction of a furan dicarboxylic dialkyl ester component with a diol component, and then performing polycondensation reaction in the presence of a titanium compound. A high-molecular-weight polyester resin can be produced using, as raw material, 2,5-furan dicarboxylic acid ester which is producible from a biomass raw material, and an industrially useful material excellent in heat resistance and mechanical physical properties can be thus provided. On the other hand, the molecular weight of the polyester resin leaves still much to desire, as does the polymerization time to achieve a reasonably high molecular weight.
Thus, the inventors found that polymers and copolymers having a 2,5-furandicarboxylate moiety within the polymer backbone, and polyesters in particular cannot be made at reasonably high molecular weight (number average molecular weight of at least 10.000) without suffering from byproducts that give rise to a yellow, greenish or brown color. On the other hand, the above references clearly show that there is a demand for polymers based on renewables to replace polyesters such as PET that are produced from petrochemicals. Thus, there is a need for a process for the production of polymers and copolymers having a 2,5-furandicarboxylate moiety within the polymer backbone which avoids the formation of such byproducts. This has now been achieved.